The present invention relates to the problem of coalescing finely dispersed droplets of oil in water, in a similar manner to the flocculation process described in U.S. Pat. No. 3,487,928.
Finely dispersed particles of oil in water are commonly found in the slop tanks of oil tankers. They derive particularly from the washing of oil cargo tanks by vigorously spraying sea water against the tank walls and bottom. Water must be separated from the oil and the oil recovered in order to avoid pollution of the sea. This is commonly done in conjunction with a loading and handling method commonly known as "Load-on-Top." Water-oil mixtures are pumped into slop tanks were separation occurs. When very small droplets are present, the separation by gravity is extremely slow and some assistance is required in order to effect an essentially complete separation. In the prior art patent cited above, a method is disclosed for agglomerating these fine droplets by means of a flocculating agent comprising a sodium montmorillonite clay applied along with a cationic organic agent or glycol. The organic agents create a lipophilic surface on the clay which tends to acquire the small oil droplets. They bridge over to form larger drops which rise and form a distinct oil phase which can be readily separated.
The interaction of the cationic agent with the clay is believed to be an ion exchange mechanism wherein the sodium ion of the clay is exchanged for the cation of the organic agent. The prior art agent is quite effective in fresh water, but less so in sea water. It is believed that in sea water the presence of sodium ions hinders the ion exchange mechanism necessary to attach the cationic agent to the clay surface. Thus, the combination of clay and cationic agents is less effective in sea water than in fresh water. One of the objectives of the present invention is to provide a substitute flocculating agent which is particularly effective in sea water.
Another disadvantage of the prior art flocculating agent is that it requires that the separate addition of a dry ingredient, i.e. the clay, and a liquid cationic agent. Proper mixing of the relatively small quantities of these ingredients in the large oil tanks made them less desirable than a single packaged ingredient which could be added with more precision and more uniformly. Another objective of the present invention is to provide a single package flocculating agent which may be used effectively onboard oil tankers.
The dry powder flocculating agent which is the subject of the present invention satisfies the foregoing requirements, being particularly effective in sea water when used aboard oil tankers.